Sennheiser Digital 9000 Instruction Manual page 109

Cleaning and maintaining the Digital 9000 system
Cleaning the L 60 charger
Remove all accupacks from the charging compartments.
Before cleaning, disconnect the NT 3-1 mains unit from the mains.
Use a dry cloth for cleaning.
Use a brush or similar to remove dust from the charging compartments.
Clean the charging contacts from time to time using e.g. a cotton swab.
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